U.S. Pat. No. 8,100,986 issued on Jan. 24, 2012 to inventor Gregor Puchhammer of Vienna (AT) shows a mechanical prosthetic finger with a proximal member, a medial member and a distal member all mounted pivotally on one another. A moveable balance arm is connected via leavers to the proximal member and to the distal member. However the Puchhammer ‘986’ reference does not show the simpler arrangement of a screw nut assembly in a proximal element cavity having a left and right pivot boss extending through the left and right slots in the proximal element cavity. The left and right pivot boss are each sized to provide free longitudinal movement within its respective left guide and right slots so as to prevent the screw nut assembly from rotating in the proximal element cavity as the screw nut assembly is moved longitudinally in the proximal element cavity by an axial screw drive.
U.S. Pat. No. 5,888,246 issued Mar. 30, 1999 to inventor David J. Gow of Edinburgh (GB) from application Ser. No. 08/702,605 filed Mar. 10, 1995. The ‘246’ patent is related art but it fails to show a screw nut assembly in a proximal element cavity having a left guide and pivot boss extending through the left slot and a right guide and pivot boss extending through the right slot of the proximal element cavity. The left and right pivot boss are each sized to provide free longitudinal movement of the left and right boss toward the distal element or toward the knuckle end of the proximal element within its respective left guide or right guide while preventing the screw nut assembly from rotating in the proximal element cavity as the screw nut assembly is moved longitudinally in the proximal element cavity by a direct longitudinal screw drive.
Mechanical fingers for artificial hands require various features to best perform the functions for an upper limb prosthetic user. The required features and functions include a high strength force generator, a light weight, good reliability, adequate speed, and a size that permits a cover that provides a natural appearance. These features are made difficult to include by the small space available inside an individual finger.
Another feature that is difficult to achieve in the design of a prosthetic mechanical finger is the short section where the prosthetic finger attaches to the residual end of the finger on the patient. Previous embodiments have placed the force generators or a part of the drive mechanism inside the build height which extends the length of the prosthetic to a position that is outside of the natural envelope of a finger. A longer than natural build height tends to result in fewer patients being fitted with a prosthetic finger. The shorter build height made possible by the invention is expected to improve the market acceptance of the prosthetic with expanded sales including sales to females and teenagers.
Another feature made possible by the invention prosthetic is a reduced cost flowing from its reduced complexity. Earlier embodiments have higher part counts with parts of significant complexity that contributed to a higher price for the prosthetic.